Hand tools that use reciprocating linear motion to produce rotational motion are known. Typical of these are the well known screwdrivers with helical grooves in an operating shaft. Among the problems with screwdrivers of that type are that the helical grooves around the operating shaft are exposed and they become dirty which greatly increases friction during operation of the tool with a corresponding reduction in torque that can be generated from operating the handle. In addition the helical grooves require lubrication which in turn causes the tool to have an exposed, oily shaft that is dirty and sticky enough to readily pickup dust and soil. The exposed helical grooves also are a danger in that an operator's skin can be caught between the handle and the rotating helical shaft. The greatest problem with such tools is that high torque cannot be obtained because the torque-producing components must operate with a lever arm that is equal to or less than the radius of the operating shaft.
U.S. Pat. No. 4,249,617 discloses a torque producing tool which mitigates many of the problems of tools having an exposed helical groove on the operating shaft. Rather than employing helical grooves on an operating shaft the tool disclosed in U.S. Pat. No. 4,249,617 employs a smooth shaft surrounded by a concentric housing having helical slots through which projections from the shaft protrude. Thus, moving the housing with reciprocal motion causes the shaft to rotate. The device can be made with bearings on the projections and resultant low friction operation does not diminish the torque produced by the reciprocal motion of the housing containing the helical slots. In addition, the housing can be made of a material such as nylon or polyvinylchloride that have natural lubricity.
The housing may also be spaced quite far from the center of the operating shaft whereby mechanical advantage is greaty increased by the length of the extensions from the operating shaft.
Although the device disclosed in U.S. Pat. No. 4,249,617 mitigates the problems found in tools having helical grooves on the operating shaft, its particular construction causes others. In order to have a tool that can rotate both clockwise and counterclockwise it is necessary to have two helical slots which run in opposite directions. On the familiar tools having helical grooves on the operating shaft the grooves simply intersect. However, in order to have opposite helical slots in a surrounding housing it is necessary that the slots do not intersect in that such intersections would weaken the housing. With the tool of U.S. Pat. No. 4,249,617 the slots are placed so that they do not intersect but in so placing the slots each thrust of the housing can only produce about 180.degree. of rotation in the shaft. It is desirable to have each thrust of the housing produce a 360.degree. rotation of the shaft and it is also desirable, in order to produce high torque, to have the force causing reciprocal motion of the handle to be capable of accepting the entire body weight of the operator whereas in the tool disclosed in U.S. Pat. No. 4,249,617 motivating force causing reciprocating motion of the housing is limited to the force of the operator's hand grip.